CST8177 - Linux II
More Scripting and sed 
 
Todd Kelley 
kelleyt@algonquincollege.com 

CST8207 - Todd Kelley 

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.World writeable files on CLS 

.More Shell Scripting (Sobel Chapter 27) 

.for loop 

.while loop 

.until loop 


.sed stream editor basics  


 
     

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Today's Topics





.The CLS is a multi-user Linux machine 

.World-writeable files are bad  mmmK? 

.Check your account on the CLS to make sure you have no file with "w" permission for "other": 

.try the find command with -perm /o+w see man find 


.From the CLS sysadmin: 


"I might put it into all marking scripts to find files with "other" write permissions and deduct 10% from the current assignment if it finds any." 
.You too possibly will some day be a system administrator trying to keep a multi-user system running properly 



World Writeable Files
CST8177 - Todd Kelley 

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.shebang line: #!/bin/sh -u 

.umask 

.set PATH 

.set locale (LC_LANG, LC_COLLATE, LC_CTYPE, LANG) 

.positional parameters ($#,$*,$0,$1,$2,etc) 

.reading input from the user (read [-p str] var[s]) 

.test program (test,[ two names, same thing) 

.if statements 



Shell scripting inventory so far
CST8177 - Todd Kelley 
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#!/bin/sh -u 
PATH=/bin:/usr/bin ; export PATH 
umask 022 
unset LC_ALL                # unset the over-ride variable 
LC_COLLATE=en_US.utf8 ; export LC_COLLATE 
LC_CTYPE=en_US.utf8 ; export LC_CTYPE 
LANG=en_US.utf8 
echo "You passed $# arguments, and those are:$*:" 
if [ $# -eq 0 ]; then 
    echo "You didn't give me much to work with" 
else 
    echo -n "Here are the arguments capitalized:" 
    echo "$*" | tr '[[:lower:]]' '[[:upper:]]' 
fi 
 

Example 1: capitalize.sh
CST8177 - Todd Kelley 

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#!/bin/sh -u 
PATH=/bin:/usr/bin ; export PATH 
umask 022 
unset LC_ALL                # unset the over-ride variable 
LC_COLLATE=en_US.utf8 ; export LC_COLLATE 
LC_CTYPE=en_US.utf8 ; export LC_CTYPE 
LANG=en_US.utf8 
if [ $# -ne 1 ]; then 
    echo 1>&2 "$0: Expecting 1 argument; found $# ($*)" 
else 
    read -p "Enter your string:" userString 
    if [ "$userString" = "$1" ]; then 
        echo "The string you entered matches the argument" 
    else 
        echo "The string you entered does not match the argument" 
    fi 
fi 
 

Example 2: match.sh
CST8177 - Todd Kelley 
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for name [ in word... ] ; do list ; done 
 
.name is a variable name we make up 

.name is set to each word... in turn, and list is exectuted 

.if [ in word... ] is omitted, the positional parameters are used instead 


 
 

For loop
CST8177 - Todd Kelley 

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for f in hello how are you today; do 
   echo "Operating on $f" 
done 

For loop example
CST8177 - Todd Kelley 
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while command; do 
   # this code runs over and over 
   # until command has  
   # non-zero exit status 
done 

While loop
CST8177 - Todd Kelley 

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while read -p "enter a word: " word; do 
    echo "You entered: $word" 
done 

While loop example
CST8177 - Todd Kelley 
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."opposite" of while 


until [ "$word" = END ]; do 
   read -p "Enter a word:" word 
   echo "You entered $word" 
done 

Until loop
CST8177 - Todd Kelley 

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.we'll use sed to read lines from stdin or a file, and write the modified lines to stdout 

.we'll concentrate on the forms 

.sed 's/this/that/' 

.replace first instance of this with that 


.sed '/^#/s/this/that/' 

.on lines that begin with # replace first instance of this with that 


.sed 's/this/that/g' 

.replace all instances of this with that 


.sed -e 's/this/that/' -e 's/what/who/' 

.replace first instance of this with that and first instance of what with who   




  

Basic sed
CST8177 - Todd Kelley 
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.echo this | sed 's/this/that/' 


that 
.echo this and this | sed 's/this/that/' 


that and this 
.echo this and this | sed 's/this/that/g' 


that and that 
.echo this and what | sed -e 's/this/that/' -e 's/what/why/' 


that and why 
.echo this and that | sed -e 's/this/that/' -e 's/that/why/g' 


why and why 
 

Sed examples
CST8177 - Todd Kelley 

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